Field of the Invention
The present invention relates to a wavelength converting member which is used with a light emitting element like light emitting diode (LED) and laser diode (LD).
Description of the Related Art
From the viewpoint of saving electric power, having long lifetime and small size, or the like, LED is applied for a cellular phone or various display devices. Further, in accordance with an improvement of light emitting efficiency in recent years, attention is drawn to its use in lighting application, and thus it is quite rapidly spreading.
At present, a main mode of white LED lighting employs a method of obtaining white light by mixing light emission by blue LED with exit light from a fluorophore which receives the incident light of the blue light and emits yellow color as a complementary color of blue color. As a wavelength converting member in which such fluorophore is used, those having fluorophore powders dispersed in a resin have been generally used. However, from the viewpoint of heat resistance, a composite of ceramics is widely used in recent years.
However, in an LED lighting required to have even emission color, the wavelength converting member based on the aforementioned composite of ceramics has a problem that it easily yields color unevenness.
In this regard, in JP 2010-157637 A, for example, a wavelength converting member having a member surface which has been processed to have irregularities to scatter, by reflection or refraction in random direction, the secondary light after wavelength conversion for resolving unevenness in luminance and unevenness in color is disclosed.
Specifically, it is described that, according to a wet etching treatment of a sintered body of inorganic materials and a fluorophore to have a configuration in which fluorophore grains are dissolved preferentially, random irregularities are formed on a surface, and the fluorophore grains are separated from the surface, the scattering property of the secondary light can be enhanced.
Further, as a conventional fluorophore which emits yellow light by receiving blue light used for white LED lighting, a YAG (yttrium•aluminum•garnet)-based fluorophore containing Ce (cerium) is known, for example. When the YAG-based fluorophore is illuminated with blue light, the illuminated blue light and the fluorescent color emitted from the YAG-based fluorophore are admixed with each other, and thus white color can be obtained.
However, in the wavelength converting member having a surface roughened by an etching treatment described in JP 2010-157637A, an etching rate difference exists between the fluorophore grains and inorganic substances. As such, a surface layer mainly composed of the inorganic substances is formed in accordance with dissolving of the fluorophore grains.
Accordingly, an uneven distribution in concentration of the fluorophore grains occurs within a surface of the wavelength converting member, and thus it cannot be said that there is a sufficient improvement of color unevenness of the light emitted from the surface.
Furthermore, there is a technical problem that, according to erosion of the fluorophore grains caused by the etching treatment, the crystallinity of the surface layer of fluorophore grains is lowered and sufficient light emitting efficiency is not obtained.
There is also a technical problem that, due to severe irregularities on the surface of the inorganic substances, the mechanical strength is poor so that cracks may easily occur during mounting or use.